OBD-II Code P0284 — What It Means & How to Fix It

What Does This Error Mean?

P0284 means Cylinder 8 is not contributing its expected share of engine power — a cylinder contribution or balance fault. The ECM detects this by monitoring tiny variations in crankshaft rotation speed after each cylinder fires. If Cylinder 8's power contribution falls short, P0284 is stored. The cylinder is still igniting — it's just underperforming. Typical symptoms include a subtle vibration at idle, slightly rough engine feel, modestly reduced power, and slightly worse fuel economy.

Affected Models

All vehicles 1996+ with 8 or more cylinders
Common in V8 trucks, SUVs, and muscle cars
Common in V8 and V10 fleet vehicles
More prevalent in high-mileage vehicles with deferred rear-bank maintenance

Common Causes

Worn or fouled spark plug on Cylinder 8 producing weak or incomplete combustion
Failing ignition coil on Cylinder 8 generating insufficient spark energy
Partially clogged fuel injector on Cylinder 8 delivering less fuel than needed
Low compression in Cylinder 8 from worn piston rings, a damaged valve, or head gasket failure
Small vacuum leak near the Cylinder 8 intake runner creating a lean condition in that cylinder

How to Fix It

Inspect and replace the Cylinder 8 spark plug. On most V8 engines, Cylinder 8 is at the rear of the driver-side bank and is often the most neglected plug on the engine due to difficult access. Examine its condition compared to front-bank plugs.

A plug that's heavily carboned, oil-fouled, or has excessive electrode gap is almost certainly the culprit. Replace the full set of plugs at the same time.
Swap the Cylinder 8 ignition coil with a coil from a different cylinder. Clear the fault codes and drive. If the balance fault moves to the new cylinder location with the swapped coil, the Cylinder 8 coil is bad. Replace it.

The coil swap test is a no-cost diagnostic tool that definitively answers whether the coil is responsible.
Have the Cylinder 8 injector professionally flow-tested. A restricted injector may fire and pass an electrical test while still flowing less fuel than the engine requires for proper combustion. Cleaning may restore flow; replacement may be necessary for heavily fouled injectors.

A flow-rate test measures actual fuel delivery — it's more diagnostic than a simple resistance check.
Inspect the intake manifold area near Cylinder 8 for vacuum leaks. The rear of the intake manifold is a common leak point — end-cap gaskets, vacuum line connections, and manifold-to-head joints all age and crack on high-mileage engines.

A smoke test is the most reliable leak-detection method. Ask your shop to perform one if you suspect a leak but can't locate it visually.
Run a compression test on all cylinders and compare results. Cylinder 8 should read within 10% of the highest cylinder. Low compression on Cylinder 8 requires professional evaluation — internal engine repairs are likely needed.

Always follow low compression with a leak-down test for a definitive cause: rings, intake valve, exhaust valve, or head gasket.

When to Call a Professional

If spark plug and coil replacement don't resolve P0284, have a mechanic perform a compression and leak-down test on Cylinder 8. Low compression indicates internal engine wear that can't be fixed with tune-up parts. A contribution fault left unresolved typically progresses to a full misfire, which can destroy a catalytic converter within days of continuous misfiring.

Frequently Asked Questions

Is P0284 only on V8 engines?

No — any engine with 8 or more cylinders can produce P0284. That includes V8, V10, and V12 gasoline engines as well as diesel V8s. V8 engines are just the most common type that drivers encounter, so P0284 appears most frequently on V8 vehicles.

How long can I drive with P0284?

You shouldn't drive indefinitely with a balance fault active. While the vehicle won't immediately break down, the underlying cause will worsen. As the contributing cylinder degrades further, you'll eventually get a full misfire. A week or two to arrange repairs is reasonable — months of procrastination is not.

How much does it cost to fix P0284?

Spark plugs: $50–$150 installed. Ignition coil: $50–$200 installed. Injector cleaning: $50–$100. Injector replacement: $150–$400. Engine compression/internal work: $1,000–$4,000+.